Transmission devices known from practice typically comprise at least one hydraulic system, which is equipped with a lubrication circuit for cooling and lubrication. In addition, the hydraulic systems are designed with cooling devices, by means of which the temperature of the hydraulic fluid led into the hydraulic system can be controlled. In order to provide a requested cooling capacity, under certain circumstances, a volume flow of hydraulic fluid to be led through the cooling device is significantly greater than a volume flow of hydraulic fluid required for the cooling and lubrication of a transmission device. For this reason, the volume flow of hydraulic fluid led through the cooling device for the temperature control of the hydraulic fluid is used only partially in the lubrication circuit for the cooling and lubrication of the transmission device. The other portion of the volume flow of hydraulic fluid led through the cooling device is introduced downstream of the cooling device and upstream of the lubrication circuit in an oil sump of the transmission device, but this brings about undesirably high heat losses.
For hybrid vehicle drive trains with at least one internal combustion engine and at least one electric engine, through an engine decoupler, the internal combustion engine is connectable to, or separable from, the remaining drive train for the representation of different operating states of a hybrid vehicle drive train. With correspondingly designed vehicle concepts, such an engine decoupler is able to be supplied through a lubrication circuit of a hydraulic system of a transmission device for cooling and lubrication with hydraulic fluid. However, this is able to be realized only with a sufficiently high volume flow of hydraulic fluid to be led through the lubrication circuit with correspondingly high heat losses, which in turn impair the overall efficiency of a transmission device to an undesirable extent. In addition, lubrication circuits of existing hydraulic systems for the volume flows of hydraulic fluid necessary for this must be dimensioned in a correspondingly large size, but this is complex and precludes the use of existing transmission hydraulic concepts.